The present invention relates to methods of using compounds as non-nucleoside inhibitors of reverse transcriptase (RT) that are effective against human immunodeficiency virus (HIV), including mutant strains of HIV, and effective in the treatment of multi-drug resistant HIV infection.
Agents currently used to treat HIV infection attempt to block replication of the HIV virus by blocking HIV reverse transcriptase (RT) or by blocking HIV protease. Three categories of anti-retroviral agents in clinical use are nucleoside analogs (such as AZT), protease inhibitors (such as nelfinavir), and the recently introduced non-nucleoside reverse transcriptase inhibitors (NNI), such as nevirapine.
The recent development of potent combination anti-retroviral regimens has significantly improved prognosis for persons with HIV and AIDS. Combination therapies are a significant factor in the dramatic decrease in deaths from AIDS (a decrease in death rate as well as absolute number). The most commonly used combinations include two nucleoside analogs with or without a protease inhibitor.
Nevirapine is currently the only NNI compound, which has been used in combination with AZT and/or protease inhibitors for the treatment of HIV. A new series of effective drug cocktails will most likely involve other NNIs in combination with nucleoside and protease inhibitors as a triple action treatment to combat the growing problem of drug resistance encountered in single drug treatment strategies.
The high replication rate of the virus unfortunately leads to genetic variants (mutants), especially when selective pressure is introduced in the form of drug treatment. These mutants are resistant to the anti-viral agents previously administered to the patient. Switching agents or using combination therapies may decrease or delay resistance, but because viral replication is not completely suppressed in single drug treatment or even with a two-drug combination, drug-resistant viral strains ultimately emerge. Triple drug combinations employing one (or two) nucleoside analogs and two (or one) NNI targeting RT provide a very promising therapy to overcome the drug resistance problem. RT mutant strains resistant to such a triple action drug combination would most likely not be able to function.
Dozens of mutant strains have been characterized as resistant to NNI compounds, including L1001, K103N, V106A, E138K, Y181 C and Y188H. In particular, the Y181 C and K103N mutants may be the most difficult to treat, because they are resistant to most of the known NNI compounds.
Recently, a proposed strategy using a knock-out concentration of NNI demonstrated very promising results. The key idea in this strategy is to administer a high concentration of NNI in the very beginning stages of treatment to reduce the virus to undetectable levels in order to prevent the emergence of drug-resistant strains. The ideal NNI compound for optimal use in this strategy and in a triple action combination must meet three criteria:
1) very low cytotoxicity so it can be applied in high doses;
2) very high potency so it can completely shut down viral replication machinery before the virus has time to develop resistant mutant strains; and
3) robust anti-viral activity against current clinically observed drug resistant mutant strains.
In recent years, structure-based drug design has played an increasingly important role in the development of useful anti-AIDS drugs as seen in the success of HIV protease inhibitor design as disclosed in Deek et al., xe2x80x9cHIV-1 Protease Inhibitorsxe2x80x9d, J. Acquired Immune Defic. Syndr. Res. Human Retrovirus, 98:145-185 (1997). Rational drug design is most effective when detailed structural information about the protein-inhibitor complex is available, a requirement which can be a limitation for reverse transcriptase.
While qualitative assessments of RT-inhibitor complexes provide helpful information in the absence of crystal structures, a systematic quantitative prediction of inhibitory activity of new compounds based on available structural information remains a challenge as discussed in Kroeger Smith et al., xe2x80x9cMolecular Modeling Studies of HIV-1 Reverse Transcriptase Nonnucleoside Inhibitors: Total Energy of Complexation as a Predictor of Drug Placement and Activityxe2x80x9d, Protein Science, 4:2203-2222 (1995).
Further, while qualitative assessments of RT-inhibitor complexes have provided helpful information in the development of non-nucleoside inhibitors (NNIs), NNIs to date fail to provide potent inhibition of RT with minimal cytotoxicity. In addition, NNIs to date fail to effectively inhibit known, drug-resistant strains of HIV.
What is needed in the art is new antiviral drugs, which have the following characteristics: (1) potent inhibition of RT; (2) minimum cytotoxicity; and (3) improved ability to inhibit known, drug-resistant strains of HIV.
It has been discovered that certain thiourea compounds of the present invention demonstrate improved potent and specific antiviral activity compared to known therapeutic agents. The thiourea compounds of the present invention possess the ability to inhibit replication of RT with minimum cytotoxicity. Further, the thiourea compounds of the present invention possess an improved ability to inhibit known, non-nucleoside resistant and drug-resistant strains of HIV.
In one aspect, the present invention is directed to piperidinylethyl-substituted, phenoxyethyl-substituted, and fluorophenethyl-substituted thiourea compounds, which inhibit non-nucleoside resistant or drug-resistant reverse transcriptase (RT) and which inhibit replication of a retrovirus, such as human immunodeficiency virus-1 (HIV-1).
The present invention is further directed to a method for inhibiting non-nucleoside resistant or drug-resistant reverse transcriptase activity of a retrovirus, such as HIV-1, comprising contacting the retrovirus with a thiourea compound of the present invention. The present invention is also directed to a method for inhibiting replication of a non-nucleoside resistant or drug-resistant retrovirus, such as HIV-1, comprising contacting the retrovirus with a thiourea compound of the present invention. In addition, the present invention is directed to a method for treating a non-nucleoside resistant or drug-resistant retroviral infection in a subject, such as an HIV-1 infection, comprising administering a thiourea compound of the invention to the subject.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
It has been discovered unexpectedly that certain substituted thiourea compounds possess increased activity against non-nucleoside resistant or drug-resistant HIV while maintaining low levels of cytotoxicity. As such, these compounds are particularly useful as active agents for antiviral compositions and for methods of treating viral infections such as HIV infections. Further, the compounds exhibit improved inhibition of multi-drug resistant strains of HIV.
Definitions:
All scientific and technical terms used in this application have meanings commonly used in the art unless otherwise specified. As used in this application, the following words or phrases have the meanings specified.
As used herein, a xe2x80x9cretrovirusxe2x80x9d includes any virus that expresses reverse transcriptase. Examples of a retrovirus include, but are not limited to, HIV-1, HIV-2, HTLV-I, HTLV-II, FeLV, FIV, SIV, AMV, MMTV, and MoMuLV.
As used herein, xe2x80x9creverse transcriptase (RT)xe2x80x9d refers to an enzyme having activity to effect reverse transcription of retroviral RNA to proviral DNA. One means by which RT activity can be determined is by measuring viral replication. One measure of viral replication is the p24 assay described herein.
As used herein, a compound that xe2x80x9cinhibits replication of human immunodeficiency virus (HIV)xe2x80x9d means a compound that, when contacted with HIV-1, for example, via HIV-infected cells, effects a reduction in the amount of HIV-1 as compared with untreated control. Inhibition of replication of HIV-1 can be measured by various means known in the art, for example, the p24 assay disclosed herein.
As used herein, a xe2x80x9cnonnucleoside inhibitor (NNI)xe2x80x9d of HIV reverse-transcriptase (HIV-RT) means a compound, which binds to an allosteric site of HIV-RT, leading to noncompetitive inhibition of HIV-RT activity. Examples of known nonnucleoside inhibitors of HIV-RT include, but are not limited to, tetrahydroimidazobenzodiazepinthiones (TIBO), 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio) thymines (HEPT), bis(heteroaryl)piperazines (BHAP), 2xe2x80x2-5xe2x80x2-bis-O-(tertbutyldimethylsilyl)-3xe2x80x2-spiro-5xe2x80x3-(4xe2x80x3-amino-1xe2x80x3, 2xe2x80x3-oxathiole-2xe2x80x3, 2xe2x80x3-dioxide) pyrimidines (TSAO), dihydroalkoxybenzyloxopyrimidine (DABO) and phenethylthiazolylthiourea (PETT) analogs.
As used herein, xe2x80x9cderivativexe2x80x9d means a chemical substance derivable from a parent substance by addition or substitution of components and which maintains the activity of the parent substance.
As used herein, xe2x80x9chalogenxe2x80x9d includes fluoro, chloro, bromo, and iodo.
As used herein, xe2x80x9cpharmaceutically acceptable saltxe2x80x9d refers to a salt that retains the desired biological activity of the parent compound and does not impart any undesired toxicological effects. Examples of such salts include, but are not limited to, (a) acid addition salts formed with inorganic acids, for example hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid, nitric acid, and the like; and salts formed with organic acids such as, for example, acetic acid, oxalic acid, tartaric acid, succinic acid, maleic acid, furmaric acid, gluconic acid, citric acid, malic acid, ascorbic acid, benzoic acid, tannic acid, pamoic acid, alginic acid, polyglutamic acid, naphthalenesulfonic acids, naphthalenedisulfonic acids, polygalacturonic acid; (b) salts with polyvalent metal cations such as zinc, calcium, bismuth, barium, magnesium, aluminum, copper, cobalt, nickel, cadmium, and the like; or (c) salts formed with an organic cation formed from N,Nxe2x80x2-dibenzylethylenediamine or ethylenediamine; or (d) combinations of (a) and (b) or (c), e.g., a zinc tannate salt; and the like. The preferred acid addition salts are the trifluoroacetate salt and the acetate salt. It is presumed that all compounds disclosed and/or claimed herein include their pharmaceutically acceptable salt form.
As used herein, xe2x80x9cpharmaceutically acceptable carrierxe2x80x9d includes any material which, when combined with a compound of the invention, allows the compound to retain biological activity, such as the ability to inhibit RT activity, and is non-reactive with the subject""s immune system. Examples include, but are not limited to, any of the standard pharmaceutical carriers such as a phosphate buffered saline solution, water, emulsions such as oil/water emulsion, and various types of wetting agents. Preferred diluents for aerosol or parenteral administration are phosphate buffered saline or normal (0.9%) saline. Compositions comprising such carriers are formulated by well-known conventional methods (see, for example, Remington""s Pharmaceutical Sciences, Chapter 43, 14th Ed., Mack Publishing Col, Easton Pa. 18042, USA).
The term xe2x80x9cconjugatexe2x80x9d means a complex formed with two or more compounds.
The phrase xe2x80x9ctargeting moietyxe2x80x9d means a compound which serves to deliver the compound of the invention to a specific site for the desired activity. Targeting moieties include, for example, molecules which specifically bind molecules present on a cell surface. Such targeting moieties useful in the invention include anti-cell surface antigen antibodies. Cytokines, including interleukins, factors such as epidermal growth factor (EGF), and the like, are also specific targeting moieties known to bind cells expressing high levels of their receptors.
As used herein, xe2x80x9cwild-typexe2x80x9d refers to the phenotype that is characteristic of the members of a species occurring naturally and contrasting with the phenotype of a mutant. A mutation is an event that results in a mutant phenotype. A mutation comprises an alteration of a DNA and/or RNA sequence relative to wild-type sequence. Alterations in DNA and/or RNA sequence can result in alterations of amino acid sequence. An example of a mutation in an amino acid sequence is the Y181 C mutation in HIV-1 strain A17, in which the tyrosine residue at position 181 of reverse transcriptase is replaced with cysteine. Another example is that of HIV strain RT-MDR, in which valine at position 106 of reverse transcriptase is replaced with alanine.
Compounds For Use In the Present Invention:
Compounds for use in the present invention include piperidinylethyl-substituted, phenoxyyethyl-substituted, and fluorophenethyl-substituted thiourea compounds, which inhibit reverse transcriptase (RT) and which inhibit replication of one or more retroviruses, such as human immunodeficiency virus-1 (HIV-1). Compounds include piperidinylethyl-substituted thiourea compounds as shown in Formula I below; phenoxyethyl-substituted thiourea compounds as shown in Formula II below; and fluorophenethyl-substituted thiourea compounds as shown in Formula III below: 
wherein X, Y, Z, Zxe2x80x2, and Zxe2x80x3 may each independently represent hydrogen, a halogen, or an alkyl group having up to about 6 carbon atoms, wherein at least one of X, Y, Z, Zxe2x80x2, and Zxe2x80x3 is not hydrogen; W is S or O; M and Mxe2x80x2 is each independently CH3, C2H5, F, Cl, Br, I, NO2, CN, OCH3 or OCH2CH3; and n, nxe2x80x2, nxe2x80x3 is each independently 0, 1, 2, 3, or 4. Desirably, at least one of X, Y, Z, Zxe2x80x2 and Zxe2x80x3 is a halogen or a methyl group. More desirably, at least one of X, Y, Z, Zxe2x80x2 and Zxe2x80x3 is a bromo, a chloro, or a methyl group.
Suitable piperidinyl-substituted thiourea compounds of the present invention include, but are not limited to, compounds of Formula I wherein Z is a halogen or C1-C6 alkyl, and X or Y is a methyl group. Desirably, the piperidinyl-substituted thiourea compound is one of the following: N-[2-(1-piperidinylethyl)]-Nxe2x80x2-[2-(5-bromopyridyl)]-thiourea; N-[2-(3-methylpiperidinylethyl)]-Nxe2x80x2-[2-(5-bromopyridyl)]-thiourea; Nxe2x80x2-[2-(2-methylpiperidinylethyl)]-Nxe2x80x2-[2-(5-bromopyridyl)]-thiourea; N-[2-(1-piperidinylethyl)]-Nxe2x80x2-[2-(5-chloropyridyl)]-thiourea; or N-[2-(3-methylpiperidinylethyl)]-Nxe2x80x2-[2-(5-chloropyridyl)]-thiourea.
It should be noted that the linkage between the piperidine ring and the thiourea component of the compound shown in Formula I can be a propyl linking group instead of the ethyl linking group in Formula I. One suitable compound of the present invention having a propyl linkage is N-[3-(2-methylpiperidinylpropyl)]-Nxe2x80x2-[2-(5-chloropyridyl)]-thiourea.
Suitable phenoxyethyl-substituted thiourea compounds of the present invention include, but are not limited to, compounds of Formula II wherein Zxe2x80x2 is a halogen or C1-C6 alkyl. Desirably, the phenoxyethyl-substituted thiourea compound is one of the following: N-[2-(phenoxy)ethyl]-Nxe2x80x2-[2-(5-chloropyridyl)]thiourea; or N-[2-(phenoxy) ethyl]-Nxe2x80x2-[2-(5-bromopyridyl)] thiourea.
Suitable fluorophenethyl-substituted thiourea compounds of the present invention include, but are not limited to, compounds of Formula III wherein Zxe2x80x3 is a halogen or C1-C6 alkyl. Desirably, the fluorophenethyl-substituted thiourea compound is one of the following: xcex2-fluoro[2-phenethyl]-Nxe2x80x2[2-(5-chloropyridyl)]thiourea; or xcex2-fluoro [2-phenethyl]-Nxe2x80x2[2-(5-bromopyridyl)]thiourea.
The piperidinylethyl-substituted, phenoxyyethyl-substituted, and fluorophenethyl-substituted thiourea compounds of the present invention have the ability to inhibit replication of a retrovirus, such as human immunodeficiency virus (HIV). In one embodiment, the thiourea compound inhibits replication of HIV with an IC50 of less than 1 xcexcM, as determined by p24 enzyme assay. In a further embodiment, the thiourea compound inhibits replication of HIV with an IC50 of less than 0.1 xcexcM. In yet a further embodiment, the thiourea compound inhibits replication of HIV with an IC50 of less than 0.01 xcexcM. In even yet a further embodiment, the thiourea compound inhibits replication of HIV with an IC50 of less than 0.001 xcexcM.
Compositions For Use In the Present Invention:
One or more of the above-described piperidinylethyl-substituted, phenoxyyethyl-substituted, and fluorophenethyl-substituted thiourea compounds may be combined with an acceptable carrier to form a composition. In one embodiment, the composition is a pharmaceutical composition. Compositions of the present invention are useful for prevention and treatment of retroviral infections, such as HIV infection.
Methods of Using the Compounds of the Invention:
The compounds of the present invention are useful in methods for inhibiting reverse transcriptase activity of a retrovirus. Retroviral reverse transcriptase is inhibited by contacting RT in vitro or in vivo, with an effective inhibitory amount of a compound of the present invention. The compounds of the present invention also inhibit replication of retrovirus, particularly of HIV, such as HIV-1. Viral replication is inhibited, for example, by contacting the virus with an effective inhibitory amount of a compound of the present invention.
The methods of the present invention are useful for inhibiting reverse transcriptase and/or replication of multiple strains of HIV, including mutant strains, and include treating a retroviral infection in a subject, such as an HIV-1 infection, by administering an effective inhibitory amount of a compound or a pharmaceutically acceptable acid addition salt of a compound of Formula I, II, or III. The compound or inhibitor of Formula I, II, or III is preferably administered in combination with a pharmaceutically acceptable carrier, and may be combined with specific delivery agents, including targeting antibodies and/or cytokines. The compound or inhibitor of the present invention may be administered in combination with other antiviral agents, immunomodulators, antibiotics or vaccines.
The compounds of Formula I, II, or III may be administered orally, parentally (including subcutaneous injection, intravenous, intramuscular, intrasternal, or infusion techniques), by inhalation spray, topically, by absorption through a mucous membrane, or rectally, in dosage unit formulations containing conventional non-toxic pharmaceutically acceptable carriers, adjuvants, or vehicles. Pharmaceutical compositions of the present invention may be in the form of suspensions or tablets suitable for oral administration, nasal sprays, creams, sterile injectable preparations, such as sterile injectable aqueous or oleagenous suspensions, or suppositories. In one embodiment, the compounds of the present invention may be applied intravaginally and/or topically, for example in gel form, for prevention of heterosexual transmission of HIV.
For oral administration as a suspension, the compositions may be prepared according to techniques well-known in the art of pharmaceutical formulation. The compositions may contain microcrystalline cellulose for imparting bulk; alginic acid or sodium alginate as a suspending agent; methylcellulose as a viscosity enhancer; and sweeteners or flavoring agents. As immediate release tablets, the compositions may contain microcrystalline cellulose, starch, magnesium stearate and lactose or other excipients, binders, extenders, disintegrants, diluents and lubricants known in the art.
For administration by inhalation or aerosol, the compositions may be prepared according to techniques well-known in the art of pharmaceutical formulation. The compositions may be prepared as solutions in saline, using benzyl alcohol or other suitable preservatives, absorption promoters to enhance bioavailability, fluorocarbons or other solubilizing or dispersing agents known in the art.
For administration as injectable solutions or suspensions, the compositions may be formulated according to techniques well-known in the art, using suitable dispersing or wetting and suspending agents, such as sterile oils, including synthetic mono- or diglycerides, and fatty acids, including oleic acid.
For rectal administration as suppositories, the compositions may be prepared by mixing with a suitable non-irritating excipient, such as cocoa butter, synthetic glyceride esters or polyethylene glycols, which are solid at ambient temperatures, but liquefy or dissolve in the rectal cavity to release the drug.
Dosage levels of approximately 0.02 to approximately 10.0 grams of a compound of the present invention per day are useful in the treatment or prevention of retroviral infection, such as HIV infection, AIDS or AIDS-related complex (ARC), with oral doses 2 to 5 times higher. For example, HIV infection may be treated by administration of from about 0.1 to about 100 milligrams of compound per kilogram of body weight from one to four times per day. In one embodiment, dosages of about 100 to about 400 milligrams of a compound are administered orally every six hours to a subject. The specific dosage level and frequency for any particular subject will vary and will depend upon a variety of factors, including, but not limited to, the activity of the specific compound; the metabolic stability and length of action of the compound; the age, body weight, general health, sex, and diet of the subject; the mode of administration; rate of excretion; drug combination; and severity of the particular condition.
The compounds of Formulae I, II, and III may be administered in combination with other agents useful in the treatment of HIV infection, AIDS, or ARC. For example, the compound of the present invention may be administered in combination with effective amounts of an antiviral, immunomodulator, anti-infective, or vaccine. The compound of the present invention may be administered prior to, during, or after a period of actual or potential exposure to retrovirus, such as HIV.
Conjugation to a Targeting Moiety:
Compounds of the present invention can be targeted for delivery to specific cells to be treated by conjugation of the compound to a targeting moiety. Targeting moieties useful for conjugation to the compounds of the present invention include, but are not limited to, antibodies, cytokines, and receptor ligands expressed on the cells to be treated.
Particularly useful targeting moieties for targeting the compounds of the present invention to cells for therapeutic activity include those ligands that bind antigens or receptors present on virus-infected cells to be treated. For example, antigens present on T-cells, such as CD48, may be targeted with antibodies directed against these antigens. Antibody fragments, including single chain fragments, may also be used. Other such ligand-receptor binding pairs are known in the scientific literature for targeting anti-viral treatments to target cells. Methods for producing conjugates of the compounds of the present invention and the targeting moieties are known.
Methods of Making the Thiourea Compounds of the Present Invention:
The piperidinylethyl-substituted and phenoxyyethyl-substituted thiourea compounds of the present invention may be produced as shown in Scheme 1 below. 
In Step 1 of Scheme 1, a substituted or unsubstituted 2-amino-pyridine is reacted with 1,1xe2x80x2-thiocarbonyldiimidazole in dry acetonitrile under a nitrogen atmosphere. The reaction mixture is stirred at room temperature for about 12 hours. A precipitate forms. The precipitate is filtered, washed with cold acetonitrile, and dried thoroughly under vacuum to yield a pyridinyl-substituted thiocarbonyl intermediate. It should be noted that 1,1xe2x80x2-carbonyldiimidazole can be substituted for 1,1xe2x80x2-thiocarbonyldiimidazole to produce suitable compounds of the invention.
In Step 2 of Scheme 1, the pyridinyl-substituted thiocarbonyl intermediate is added to a dry flask under nitrogen, along with anhydrous dimethylformamide. The contents are stirred for about 30 minutes at room temperature. An appropriately substituted amine, such as 1-(2-aminoethyl)-2-methyl-piperidine, dissolved in dry dimethylformamide is added to the reaction mixture. Suitable piperidinylethyl amines may be prepared by N-alkylation of substituted piperidines using bromoethyl amine.
The reaction mixture is heated to about 110xc2x0 C. over an oil bath for about 15 hours. The reaction mixture is then cooled and poured into ice water. The contents are stirred for approximately an hour. A precipitate forms. The precipitate is filtered, washed with cold water several times, and dried under vacuum. The precipitate is then added to ethyl acetate, and washed with water and brine. The ethyl acetate layer is separated from the aqueous layer, and subsequently dried over anhydrous sodium sulfate. A filtration step and evaporation of the solvent yields the desired piperidinylethyl-substituted or phenoxyyethyl-substituted thiourea compound. Compounds may be further purified using silica gel column chromatography.
The xcex2-fluorophenethyl-substituted thiourea compounds of the present invention may be produced as shown in Scheme 2 below. 
In Step 1 of Scheme 2, benzaldehyde is condensed with trimethyl silyl cyanide (TMSiCN) and zinc iodide (ZnI2) to obtain a cyano hydrin intermediate. In Step 2 of Scheme 2, the cyano hydrin intermediate is reacted with diethylaminosulfur trifluoride (DAST) in tetrahydrofuran (THF) to produce a fluoro-substituted compound, 2-fluoro-2-phenylacetonitrile. In Step 3 of Scheme 2, the fluoro-substituted compound, 2-fluoro-2-phenylacetonitrile, is further reduced using borane in ethyl ether (Et2O) to produce a fluoro-substituted amine.
In Step 4 of Scheme 2, the fluoro-substituted amine produced in Step 3 of Scheme 2 is reacted with an appropriate pyridinyl-substituted thiocarbonyl intermediate as prepared in Step 1 of Scheme 1. It should be noted that an appropriate pyridinyl-substituted carbonyl intermediate can be prepared in Step 1 of Scheme 1 by substituting 1,1xe2x80x2-carbonyldiimidazole for 1,1xe2x80x2-thiocarbonyldiimidazole. The appropriate pyridinyl-substituted carbonyl intermediate can then be used to produce a suitable compounds of Formula III. The fluoro-substituted amine produced in Step 3 of Scheme 2 is condensed with an appropriate pyridinyl-substituted thiocarbonyl intermediate in anhydrous dimethylformamide (DMF) to produce the desired fluoroethyl-substituted thiourea compound. The resulting fluoroethyl-substituted thiourea compound may be further purified using column chromatography.
Proposed Mechanism:
It is believed that the piperidinylethyl-substituted, phenoxyyethyl-substituted, and fluorophenethyl-substituted thiourea compounds of the present invention have the ability to inhibit replication of HIV strains, including multi-drug resistant HIV strains such as Y181 C and V106A, due to their positioning and interaction with sites within the composite NNI-RT binding pocket as previously described in PCT Publication WO 99/47501.
The present invention is described above and further illustrated below by way of examples, which are not to be construed in any way as imposing limitations upon the scope of the invention. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the present invention and/or the scope of the appended claims.